Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.34	6.809%	$131.7382	$131.74	$131.75	$131.70
Purchase #2	$117.32	11.727%	$131.0781	$131.08	$131.10	$131.10
Purchase #3	$191.25	9.779%	$209.9523	$209.95	$209.95	$210.00
Purchase #4	$70.66	10.714%	$78.2305	$78.23	$78.25	$78.20
Purchase #5	$184.86	10.581%	$204.42	$204.42	$204.40	$204.40
Purchase #6	$125.77	9.159%	$137.2893	$137.29	$137.30	$137.30
Purchase #7	$245.98	7.823%	$265.223	$265.22	$265.20	$265.20
7 purchase totals =	$1,059.18		$1,157.9314	$1,157.93	$1,157.95	$1,157.90